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Home > BLOG > What is hot melt adhesive? And the influence of SIS on the properties of hot melt pressure sensitive adhesive

What is hot melt adhesive? And the influence of SIS on the properties of hot melt pressure sensitive adhesive

January 03,2023

Hot-melt adhesive is a kind of polymeric adhesive which is coated in a hot-melt state and bonded by cooling and hardening. It contains no solvent, 100% solid content, and is mainly composed of thermoplastic polymer. It is a solid at room temperature, melts into a liquid when heated, and hardens rapidly when cooled to achieve adhesive bonding. Hot melt adhesive has developed rapidly in recent years, which is closely related to its characteristics such as lax surface treatment, solvent-free, rapid bonding, high production efficiency and remarkable economic effect.

Main features of hot melt adhesive:

The adhesive bonding is rapid, the whole adhesive bonding process only takes a few seconds, no pressure equipment is needed, and it is suitable for automatic continuous production with high production efficiency.
Solvent-free, generally no harmful substances are released during bonding, harmless to operators, pollution-free to the environment, no fire danger, and convenient for storage and transportation.
It can be melted and bonded repeatedly, and is suitable for some bonding with special technological requirements.
A variety of materials can be bonded.
The disadvantages of hot melt adhesive are poor thermal stability and low bonding strength. It is not suitable for bonding heat-sensitive materials. In order to achieve better results, special equipment is needed.
At present, hot melt adhesives are widely used in book binding, packaging, automobiles, consumer electronics, smart wear, smart home appliances, electronic appliances, fibers, metals, shoes and wood industries.

How to increase the initial viscosity ofSIShot melt pressure sensitive adhesive?

Plasticizer is an essential component for preparing SIS hot melt pressure-sensitive adhesive, which can improve the wettability of pressure-sensitive adhesive on the surface of adhesive material. Improve adhesion and reduce cost. Plasticizer is a liquid with low viscosity at room temperature. When used in SIS hot-melt pressure-sensitive adhesive, it can obviously reduce the melt viscosity, which is beneficial to coating construction, and at the same time increase the pressure-sensitive viscosity and initial viscosity. However, plasticizer will also reduce the cohesive strength of pressure-sensitive adhesive, and when the dosage is too much, the adhesive and peel strength will obviously decrease.
Commonly used plasticizers include naphthenic oil, white mineral oil, liquid paraffin, dibutyl (octyl) phthalate, etc., which have different effects on the properties of SIS hot melt pressure sensitive adhesive. Di-butyl (octyl) phthalate has a very good initial viscosity, but its adhesion and peel strength are poor. Naphthenic oil has good initial viscosity, long sticking time and high peeling strength, and is the plasticizer with the best comprehensive performance. White mineral oil and liquid paraffin are slightly worse than naphthenic oil as plasticizers.
Therefore, naphthenic oil is generally used as plasticizing agent when preparing SIS hot melt pressure sensitive adhesive, and sometimes better results will be obtained if compound plasticizer is used.

 Effect of plasticizer on the properties of SIS hot melt pressure sensitive adhesive

Plasticizer is an essential component for preparing SIS hot-melt pressure-sensitive adhesive, which can improve the wettability of pressure-sensitive adhesive on the surface of adhesive material. Improve adhesion and reduce cost. Plasticizer is a liquid with low viscosity at room temperature. When used in SIS hot-melt pressure-sensitive adhesive, it can obviously reduce the melt viscosity, which is beneficial to coating construction, and at the same time increase the pressure-sensitive viscosity and initial viscosity. However, plasticizer will also reduce the cohesive strength of pressure-sensitive adhesive, and when the dosage is too much, the adhesive and peel strength will obviously decrease.
Commonly used plasticizers include naphthenic oil, white mineral oil, liquid paraffin, dibutyl (octyl) phthalate, etc., which have different effects on the properties of SIS hot melt pressure sensitive adhesive. Di-butyl (octyl) phthalate has a very good initial viscosity, but its adhesion and peel strength are poor. Naphthenic oil has good initial viscosity, long sticking time and high peeling strength, and is the plasticizer with the best comprehensive performance. White mineral oil and liquid paraffin are slightly worse than naphthenic oil as plasticizers.
Therefore, naphthenic oil is generally used as plasticizing agent when preparing SIS hot melt pressure sensitive adhesive, and sometimes better results will be obtained if compound plasticizer is used.
With the increase of plasticizer content, the initial viscosity of the prepared hot-melt pressure-sensitive adhesive becomes better, and the 180 peel strength decreases obviously. This is because plasticizer has poor compatibility with hard segment of elastomer, but good compatibility with rubber segment, which makes the volume of rubber phase increase, thus increasing the sensitivity to pressure. At the same time, due to the decrease of the force between the molecules in the rubber phase, it is easy to creep between the adhesive and the adhered material, which leads to the decrease of the adhesive and 180 peel strength.

The influence of 3.SIS parameters on the properties of hot-melt pressure-sensitive adhesive

Thermoplastic elastomer SIS is a block copolymer of styrene and isoprene. Its molecular structure is similar toSBS, and it is made up of three segments: polystyrene segment (S)- polyisoprene segment (I)- polystyrene segment (S), so it is called SIS. Its technical parameters mainly include configuration of SIS, block ratio (S/I), molecular weight and diblock SI content. According to on-line coating, due to the influence of the side chain methyl of the intermediate block polyisoprene, SIS has good cohesion and adhesion, and at the same time, it has the characteristics of low modulus, good elasticity, low melt viscosity, strong viscosity and good coating performance. Therefore, SIS is an excellent main material for preparing hot melt pressure sensitive adhesive (HMPSA), which has been widely used in the production of pressure sensitive adhesive tape and label paper.
HMPSA refers to a semi-dry solid which is coated on a substrate when heated to a molten state and has permanent viscosity after cooling. SIS hot melt pressure sensitive adhesive is generally made by mixing SIS plasticizer and tackifying resin in a certain proportion and melting at about 18℃. Its properties are mainly characterized by initial viscosity, holding viscosity and 180 peel strength. In addition, the softening point, slitting performance and melt viscosity of HMPSA are often the properties that users are concerned about. Due to the diversity and particularity of market requirements for SIS products and HMPSA performance, SIS technical parameters will have a certain impact on the performance of hot-melt pressure-sensitive adhesive.